In the previous notebook, we retrieved VOEvents related to a Swift XRT
detection using the cone-search filter. A cone-search can bring to light
new associations between VOEvents from different observatories, but we
saw that it can also return unrelated events that just happen to lie
nearby.

** This notebook shows how to explore relations between VOEvents which
are already encoded by the packet author, using the ‘citation’
mechanism. **

It also includes a short example using networkx to visualise a
citation-network.

Aha! So, the original BAT GRB trigger is the ‘anchor reference’ for all
these other packets. Are any of them cited, in turn? There’s a quick way
to find out; we can use the ivorn_cited_count endpoint to get a
citation count for all the packets matching our current filter set:

So we have quite a boring citation network - several packets cite the
BAT GRB position, then the trail ends. Nonetheless, we can use it to
show off a party trick - voeventdb.remote contains an extra function
that makes repeated calls to the server to perform a depth-first
search (with
configurable maximum recursion level) of the citation network: